Video telephone service has long been desired by consumers (assuming that marketing studies can be believed) because it enhances the communication process, and by manufacturers (assuming that the profit motive is alive and well) because of the business opportunities presented. Such service was even predicted to be commonplace by the year 2001 according to the Stanley Kubrick film classic "2001--A Space Odyssey" in which an AT&T Picturephone was used to illustrate communication service 30 years in the future. The technical challenge that underlies video telephone service has to do with transmitting a tremendous amount of data over a conventional telephone channel--like filling a large swimming pool with a small garden hose. Figuratively speaking, the Picturephone solution was to use a very large (non-standard) hose which was not easily made available to residential customers, and too expensive when it was.
Over the past twenty years, advances in communications have made it possible to transmit at very high data rates over the Public Switched Telephone Network (PSTN), and advances in data compression have enabled the transmission of audio and video information with much less data than was originally thought necessary. Nevertheless, each PSTN channel only provides approximately 3300 Hz bandwidth which is tolerable for audible communications (20,000 Hz bandwidth is typical for high fidelity sound systems); but when video information (normally 4,000,000 Hz bandwidth) is added, the mere consideration of a PSTN channel for the task of transmitting both would be in the realm of fantasy. Indeed, it may never be possible to duplicate the quality of conventional broadcast television which consumers now expect, but it may be acceptable to reduce the size of the video screen, picture resolution, and frame rate in order to provide a video telephone product that connects to standard telephone lines. Unfortunately, even reducing all of the above leads to a result which many customers are still not comfortable with--particularly when the cost is substantially higher than a telephone set.
Conventional television sets update an entire video picture with a new "frame" 30 times per second, and each frame is subdivided into two fields which are alternately displayed. Accordingly, 60 fields per second are presented to the viewer, each having half the information of the full frame. Because these fields are interlaced, and because the information between adjacent lines is quite similar, a visual effect known as "flicker" is virtually eliminated. However, because them is only a small amount of motion during a video telephone conversation, it is possible to reduce the frame rate while preserving the appearance of continuous motion. Furthermore, video picture size can be reduced because the user is generally close to the video telephone set during a conversation, and the number of picture elements (pixels) required to fill the frame is correspondingly reduced. By taking advantage of the opportunities to reduce picture quality with minimum perceived effect, it is now possible to simultaneously transmit color video pictures and audio information over standard telephone lines. However, the frame rate possible is only in the range of 2-10 frames per second and motion is unnaturally abrupt. Accordingly, more needs to be done to make video telephony acceptable to demanding consumers.
It is, therefore, desirable to provide a video telephone set that operates over standard telephone lines with increased frame rate.